The present application relates to an arithmetic circuit, a signal selection method, and a computer program.
Recently, information processing terminals that can communicate with a noncontact reading and writing device (reader/writer), such as a noncontact IC (Integrated Circuit) card (hereinafter, referred to as “IC card”) and a cellular phone having an IC card function have been in widespread use. The reading and writing device and the information processing terminal use a magnetic field (carrier wave) at a specific frequency of 13.56 MHz, for example, for communication and perform transmission and reception of data using the carrier wave. A noncontact communication system using the information processing terminal is widely used for entry and exit processing at automatic ticket gates of stations, boarding gates of airports, etc., and payment processing in registers of sales stores, vending machines, etc.
With the widespread use of the noncontact communication system, there have been plural communication systems between terminals and reader writers. The communication systems between terminals and reader writers are divided into Type A, Type B, Type C, etc. according to the differences in modulation methods and encoding methods. However, the difference between the communication systems is not obvious for users. If it may be impossible to make noncontact communication due to the difference in communication system even when the IC card, the cellular phone, or the like is held over the reader writer, the users find it inconvenient. Accordingly, communication devices and communication methods for supporting plural communication systems have been developed and technologies relating to the communication devices and communication methods have been disclosed (e.g., see JP-A-2008-35104 and JP-2008-269368).